#include <bits/stdc++.h>
using namespace std;
void wa_haya_exe();
void solve();

int main() {
   wa_haya_exe();
   solve();
}

// --------------------------------------------------------------------------------------------------------------

#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

void wa_haya_exe() {
   cin.tie(nullptr);
   ios::sync_with_stdio(false);
}

mt19937 Random() {
   random_device seed_gen;
   mt19937 engine {seed_gen()};
   return engine;
}

// --------------------------------------------------------------------------------------------------------------

// alias
template <class T> using V = vector<T>;
template <class T,class U> using P = pair<T,U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqr = priority_queue<T,vector<T>,greater<T>>;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
using uint = unsigned;
using pi = P<ll,ll>;
using pd = P<ld,ld>;
using pc = P<char,char>;
using ps = P<string,string>;

// Input
template <class T> void scan(T& a) { cin >> a; }
template <class T,class U> void scan(pair<T, U>& p) { scan(p.first); scan(p.second); }
template <class T> void scan(V<T>& a) { for(auto &i: a) scan(i); }
void in(){}
template <class Head, class... Tail> void in(Head& head, Tail&... tail) { scan(head); in(tail...); }
#define INT(...) int __VA_ARGS__;in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__;in(__VA_ARGS__)
#define ULL(...) ull __VA_ARGS__;in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__;in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__;in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__;in(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__;in(__VA_ARGS__)

// Output
#define println(x) cout << x << endl;
#define printb(x) cout << x << " ";
#define print(x) cout << x;
#define fix(x) cout << fixed << setprecision(x);
#define NL cout << endl;
#define None println(-1)

// YesNo System
#define Yes println("Yes")
#define No println("No")
#define YesNo(bool) if(bool) Yes else No
#define YESNO(bool) if(bool) println("YES") else println("NO")
#define yesno(bool) if(bool) println("yes") else println("no")

// constance
constexpr int mod=1000000007;//*/
/*constexpr int mod=998244353;//*/
const int INF=0x3fffffff;
const ll LINF=0x1fffffffffffffff;
const ld DINF=numeric_limits<ld>::infinity();
const double PI=acos(-1);

// for
#define overload4(_1,_2,_3,_4,name,...) name
#define overload3(_1,_2,_3,name,...) name
#define rep1(n) for(ll i=0; i<n; ++i)
#define rep2(i,n) for(ll i=0; i<n; ++i)
#define rep3(i,a,b) for(ll i=a; i<b; ++i)
#define rep4(i,a,b,c) for(ll i=a; i<b; i+=c)
#define rep(...) overload4(__VA_ARGS__,rep4,rep3,rep2,rep1)(__VA_ARGS__)
#define rvp1(i,n) for(ll i=n-1; i>=0; i--)
#define rvp2(i,a,b) for(ll i=b-1; i>=a; i--)
#define rvp3(i,a,b,c) for(ll i=b-1; i>=a; i-=c)
#define rvp(...) overload4(__VA_ARGS__,rvp3,rvp2,rvp1)(__VA_ARGS__)
#define all1(v) v.begin(),v.end()
#define all2(v,a) v.begin(),v.begin()+a
#define all3(v,a,b) v.begin()+a,v.begin()+b
#define all(...) overload3(__VA_ARGS__,all3,all2,all1)(__VA_ARGS__)
#define each1(elem,v) for(auto &elem: v)
#define each2(x,y,v) for(auto &[x,y]: v)
#define each3(x,y,z,v) for(auto &[x,y,z]: v)
#define each(...) overload4(__VA_ARGS__,each3,each2,each1)(__VA_ARGS__)
#define sqrp1(n) for(ll i=0; i*i<n; ++i)
#define sqrp2(i,n) for(ll i=0; i*i<n; ++i)
#define sqrp3(i,a,b) for(ll i=a; i*i<b ++i)
#define sqrp(...) overload3(__VA_ARGS__,sqrp3,sqrp2,sqrp1)(__VA_ARGS__)
#define irp(it,v) for(auto it=v.begin(); it!=v.end(); ++it)
#define ir(it,v) for(auto it=v.begin(); it!=v.end();)
#define FE(v,f) for_each(all(v),f)

// vector
#define vec(type,name,...) vector<type> name(__VA_ARGS__)
#define Vec(type,name) vector<type> name
#define VEC(type,name,size) vector<type>name(size);in(name)
#define wec(type,name,h,...) vector<vector<type>> name(h,vector<type>(__VA_ARGS__))
#define Wec(type,name,h) vector<vector<type>>name(h)
#define WEC(type,name,h,w) vector<vector<type>> name(h,vector<type>(w));in(name)
#define rall(v) v.rbegin(), v.rend()
#define rev(v) reverse(all(v))
#define Sort(v) sort(all(v))
#define Sortt(v) sort(rall(v))
#define Min(v) *min_element(all(v))
#define Max(v) *max_element(all(v))
#define LB(v,x) lower_bound(all(v),x)
#define UB(v,x) upper_bound(all(v),x)
#define vsum(v) accumulate(all(v),0LL)
#define vdsum(v) accumulate(all(v),0.0L)
#define vmul(v) accumulate(all(v),1,[](int acc,int i) { return acc*i; })
#define unq(v) Sort(v);v.erase(unique(all(v)),v.end())
#define cp(v,w) copy(all(v),back_inserter(w))
#define smp(v,w,size,eng) sample(all(v),back_inserter(w),size,eng);
#define rpl(v,f,r) replace_if(all(v),f,r)
#define rtt(v,idx) rotate(all(v,idx),v.end())
#define All(v,f) all_of(all(v),f)
#define Exist(v,f) any_of(all(v),f)
#define Find(v,x) find(all(v),x)
#define cntif(v,f) count_if(all(v),f)
template <class T> inline T Count(V<T>& v, ll x) {
   Sort(v);
   return UB(v,x)-LB(v,x);
}
template <class T> inline void out1(V<T>& v) {
   FE(v,[](T x){printb(x)});
   NL
}
template <class T> inline void out2(V<T>& v) { FE(v,[](T x){println(x)}); }

// renew max(old < new) or min(old > new)
template <class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template <class T> bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }

// overflow
template <class T> bool overflow_if_add(T a, T b) { return (numeric_limits<T>::max() - a) < b; }
template <class T> bool overflow_if_mul(T a, T b) { return (numeric_limits<T>::max() / a) < b; }

// tips
#define elif else if
#define scp(a,x,b) a<=x&&x<=b
#define mp make_pair
#define mt make_tuple
#define bit_check(tar,bit) tar&(1<<bit)
#define bit1cnt(x) __builtin_popcountll(x)
#define str_rpl(s,a,b) regex_replace(s,regex(a),b)
template<class... T> constexpr auto mymin(T... a) {
   return min(initializer_list<common_type_t<T...>>{a...});
}
template<class... T> constexpr auto mymax(T... a) {
   return max(initializer_list<common_type_t<T...>>{a...});
}

// Permutation
template <class T> inline void nPr(V<T>& v) {
   Sort(v);
   do {
      each(num,v) printb(num);
   NL
   } while(next_permutation(all(v)));
}

// fuctorial
template <class T> inline T fct(T& n) {
   T f=1;
   rep(i,1,n+1) {
      f*=i;
   }
   return f;
}

// UnionFind-Tree (default: size)
struct UnionFind {
   V<ll> rank,parents,size;
   UnionFind(ll n) {
      rank.resize(n,0);
      parents.resize(n,0);
      size.resize(n,0);
      rep(i,n) makeTree(i);
   }
   void makeTree(ll x) {
      parents[x]=x;
      rank[x]=0;
      size[x]=1;
   }
   bool isSame(ll x, ll y) { return findRoot(x) == findRoot(y); }
   bool unite(ll x, ll y) {
      x=findRoot(x);
      y=findRoot(y);
      if(x==y) return false;
      // rank pattern
      /*if(rank[x]>rank[y]) parents[y]=x;
      else {
         parents[x]=y;
         if(rank[x]==rank[y]) rank[y]++;
      }//*/
      // size pattern
      if(size[x]>size[y]) {
         parents[y]=x;
         size[x]+=size[y];
      }
      else {
         parents[x]=y;
         size[y]+=size[x];
      }//*/
      return true;
   }
   ll findRoot(ll x) {
      if(x!=parents[x]) parents[x]=findRoot(parents[x]);
      return parents[x];
   }
   ll treeSize(ll x) { return size[findRoot(x)]; }
};

// MODINT
struct Modint{
   uint num = 0;
   constexpr Modint() noexcept {}
   constexpr Modint(const Modint &x) noexcept : num(x.num){}
   constexpr operator ll() const noexcept { return num; }
   constexpr Modint& operator+=(Modint x) noexcept { num += x.num; if(num >= mod) num -= mod; return *this; }
   constexpr Modint& operator++() noexcept { if(num == mod - 1) num = 0; else num++; return *this; }
   constexpr Modint operator++(int) noexcept { Modint ans(*this); operator++(); return ans; }
   constexpr Modint operator-() const noexcept { return Modint(0) -= *this; }
   constexpr Modint& operator-=(Modint x) noexcept { if(num < x.num) num += mod; num -= x.num; return *this; }
   constexpr Modint& operator--() noexcept { if(num == 0) num = mod - 1; else num--; return *this; }
   constexpr Modint operator--(int) noexcept { Modint ans(*this); operator--(); return ans; }
   constexpr Modint& operator*=(Modint x) noexcept { num = ull(num) * x.num % mod; return *this; }
   constexpr Modint& operator/=(Modint x) noexcept { return operator*=(x.inv()); }
   template<class T> constexpr Modint(T x) noexcept {
      using U = typename conditional<sizeof(T) >= 4, T, int>::type;
      U y = x; y %= U(mod); if(y < 0) y += mod; num = uint(y);
   }
   template<class T> constexpr Modint operator+(T x) const noexcept { return Modint(*this) += x; }
   template<class T> constexpr Modint& operator+=(T x) noexcept { return operator+=(Modint(x)); }
   template<class T> constexpr Modint operator-(T x) const noexcept { return Modint(*this) -= x; }
   template<class T> constexpr Modint& operator-=(T x) noexcept { return operator-=(Modint(x)); }
   template<class T> constexpr Modint operator*(T x) const noexcept { return Modint(*this) *= x; }
   template<class T> constexpr Modint& operator*=(T x) noexcept { return operator*=(Modint(x)); }
   template<class T> constexpr Modint operator/(T x) const noexcept { return Modint(*this) /= x; }
   template<class T> constexpr Modint& operator/=(T x) noexcept { return operator/=(Modint(x)); }
   constexpr Modint inv() const noexcept { ll x = 0, y = 0; extgcd(num, mod, x, y); return x; }
   static constexpr ll extgcd(ll a, ll b, ll &x, ll &y) noexcept { ll g = a; x = 1; y = 0; if(b){ g = extgcd(b, a % b, y, x); y -= a / b * x; } return g; }
   constexpr Modint pow(ull x) const noexcept { Modint ans = 1, cnt = *this; while(x){ if(x & 1) ans *= cnt; cnt *= cnt; x /= 2; } return ans; }
};
ostream& operator<<(ostream& os, const Modint& m){ os << m.num; return os; }

// --------------------------------------------------------------------------------------------------------------


void solve() {
 INT(n);
 int sum=0;
 rep(n+1) sum+=i;
 println(sum)
}